Valve with secondary load bearing surface

ABSTRACT

A valve ( 120 ) for controlling fluid flow therethrough in downhole applications is disclosed. The valve ( 120 ) comprises a valve housing having a valve closure mechanism ( 122 ) and a valve seat ( 124 ) disposed therein. The valve closure mechanism ( 122 ) has sealing surface ( 128 ) and a secondary load bearing surface ( 142 ). The valve seat ( 124 ) has a valve seat sealing surface ( 126 ) that mates with the sealing surface ( 128 ) of the valve closure mechanism ( 122 ). The secondary load bearing surface ( 142 ) of the valve closure mechanism ( 122 ) mates with a valve secondary load bearing surface ( 134 ) which may be supported by the valve seat ( 124 ).

RELATED APPLICATION

[0001] This application is a continuation-in-part of pending applicationSer. No. 09/309,716 filed on May 11, 1999.

TECHNICAL FIELD OF THE INVENTION

[0002] This invention relates in general to subsurface safety valvesand, in particular, to a subsurface safety valve that includes a valvesealing surface and a secondary load bearing surface.

BACKGROUND OF THE INVENTION

[0003] Without limiting the scope of the invention, the background willdescribe surface controlled, subsurface safety valves, as an example.

[0004] Surface controlled, subsurface safety valves are commonly used toshut in oil and gas wells in the event of a failure or hazardouscondition at the well surface. Such safety valves are typically fittedinto the production tubing and operate to block the flow of formationfluid upwardly therethrough. The subsurface safety valve providesautomatic shutoff of production flow in response to a variety of out ofrange safety conditions that can be sensed or indicated at the surface.For example, the safety conditions include a fire on the platform, ahigh or low flow line temperature or pressure condition or operatoroverride.

[0005] During production, the subsurface safety valve is typically heldopen by the application of hydraulic fluid pressure conducted to thesubsurface safety valve through an auxiliary control conduit whichextends along the tubing string within the annulus between the tubingand the well casing. Flapper type subsurface safety valves utilize aclosure plate which is actuated by longitudinal movement of ahydraulically actuated, tubular piston. The flapper valve closure plateis maintained in the valve open position by an operator tube which isextended by the application of hydraulic pressure onto the piston. Apump at the surface pressurizes a reservoir which delivers regulatedhydraulic control pressure through the control conduit. Hydraulic fluidis pumped into a variable volume pressure chamber and acts against thecrown of the piston. When, for example, the production fluid pressurerises above or falls below a preset level, the control pressure isrelieved such that the piston and operator tube are retracted to thevalve closed position by a return spring. The flapper plate is thenrotated to the valve closed position by a torsion spring or tensionmember.

[0006] In conventional subsurface safety valves of the type utilizing anupwardly closing flapper plate, the flapper plate is seated against anannular sealing face, either in metal-to-metal contact or metal againstan annular elastomeric seal. In one design, the flapper closure platehas a flat, annular sealing face which is engageable against a flat,annular valve seat ring, with sealing engagement being enhanced by anelastomeric seal ring which is mounted on the valve seat. In anotherdesign, the valve seat includes a downwardly facing, conical segmenthaving a sloping sealing surface and the flapper closure plate has acomplementary, sloping annular sealing surface which is adapted forsurface-to-surface engagement against the conical valve seat surface.

[0007] Typically, the flapper closure plate is supported for rotationalmovement by a hinge assembly which includes a hinge pin and a torsionspring or tension member. It will be appreciated that structuraldistortion of the flapper valve closure plate, or damage to the hingeassembly which supports the flapper closure plate, can causemisalignment of the respective sealing surfaces, thereby producing aleakage path through the safety valve.

[0008] Such misalignment will prevent correct seating and sealing of theflapper closure plate, and formation fluid may escape through thedamaged valve, causing waste and pollution. During situations involvingdamage to the wellhead, the well flow must be shut off completely beforerepairs can be made and production resumed. Even a small leak throughthe flapper safety valve in a gas well can cause catastrophic damage.

[0009] Attempts have been made to overcome this misalignment problem.For example, one design involves the use of a valve seat and an upwardlyclosing flapper plate each having a sealing surface with a matchedspherical radius of curvature. That is, the valve seat is a concavespherical segment and the sealing surface of the flapper plate is aconvex spherical segment. In this arrangement, the spherical radius ofcurvature of the concave valve seat spherical segment is matched withthe spherical radius of curvature of the convex spherical segment whichdefines the sealing surface on the flapper plate. The matching sphericalsurfaces are lapped together to provide a metal-to-metal seal along theinterface between the nested convex and concave sealing surfaces.

[0010] As such, the convex spherical sealing segment of the flapperplate is received in nesting engagement within the concave sphericalsegment surface of the valve seat, which allows some angulardisplacement of the flapper plate relative to the valve seat withoutinterrupting surface-to-surface engagement therebetween. Thus, theconcave spherical seating surface of the safety valve seat will toleratea limited amount of misalignment of the flapper plate which might becaused by structural distortion of the closure plate or warping of thehinge assembly.

[0011] It has been found, however, the even when using spherical sealingsurfaces leakage may occur. Specifically, applications using largediameter tubing and having a low ratio between the outer diameter andthe inner diameter of the sealing surfaces, distortion of the flapperclosure plate caused by increased loads on the flapper closure plate mayresult in a loss of the seal. These increased loads are developed as aconsequence of using larger safety valves having larger flapper closureplates in larger tubing.

[0012] Therefore, a need has arisen for a flapper valve that maintains aseal in a well requiring a large diameter flapper valve having a lowratio between the outer diameter and the inner diameter of the sealingsurfaces. A need has also arisen for such a flapper valve that does notexperience a loss of the seal in response to distortion of the flapperclosure plate caused by the increased loads associated with suchdesigns.

SUMMARY OF THE INVENTION

[0013] The present invention disclosed herein is a valve comprising avalve closure mechanism that mates with a valve seat, where the valvehas enhanced load-bearing capability. The valve of the present inventionhas separate sealing and load bearing surfaces, and can thus be deployedin a well requiring a large diameter valve having a low ratio betweenthe outer diameter and the inner diameter of the sealing surfaces. Theenhanced load-bearing capability of the valve of the present inventionis particularly applicable in high pressure situations. Furthermore, thevalve of the present invention does not experience a loss of the seal inresponse to distortion of the valve closure mechanism due to theincreased loads on the valve that are associated with such applications.

[0014] The valve of the present invention comprises a valve housing, avalve closure member having a sealing surface and a secondary loadbearing surface, a valve seat having a valve seat sealing surface, and asecondary load bearing surface that is located on either the valve seator as part of the valve housing or on both the valve seat and the valvehousing. The valve closure mechanism includes a secondary load bearingsurface that may be located anywhere on, or formed as an integral partof, the valve closure mechanism. The valve closure mechanism secondaryload bearing surface may be either an internal or external shoulder, orone or more internal or external support members, or any combinationthereof. The load bearing surface of the valve closure mechanism willmate or engage with a load bearing surface found either on the valveseat or the valve housing, or both.

[0015] Should the valve seat include a secondary load bearing surface,the secondary load bearing surface may be either an internal loadbearing surface of the valve seat or an external load bearing surface ofthe valve seat. The secondary load bearing surface of the valve seat maybe either an internal or external shoulder, or one or more internalsupport members, or any combination thereof. A secondary load bearingsurface may alternatively be coupled to the valve housing or integrallyformed thereon. Should the valve housing include a secondary loadbearing surface, the secondary load bearing surface of the valve housingmay, for example, be an internal shoulder or one or more internalsupport members, or any combination thereof.

[0016] The valve of the present invention may be a flapper valve.Alternatively, the valve of the present invention may be a gate valve, aball valve, a poppit, a valve having sliding members, a valve havingsleeves, and any other types of valves known in the art. Accordingly,the valve closure member of the valve may be a flapper closure plate, agate, a ball, a sleeve, a sliding member, or any other structure thatforms a seal when mated to or engaged with a corresponding valve seat.Furthermore, a flapper closure plate may be flat or contoured.

[0017] In one embodiment, the valve includes a tubular valve housinghaving a valve chamber. A valve seat is mounted within a housing. Thevalve seat has a sealing surface and a secondary load bearing surface. Avalve closure mechanism is provided as a flapper closure plate having asealing surface and a secondary load bearing surface. The flapperclosure plate is disposed within the valve chamber and rotates between avalve open position, in which the flapper closure plate is removed fromthe valve seat, and a valve closed position, in which the sealingsurface of the flapper closure plate sealingly engages the valve seatsealing surface for preventing flow therethrough. When the flapperclosure plate is in the valve closed position, the secondary loadbearing surface of the valve seat defines the maximum travel of theflapper closure plate.

[0018] In one embodiment of the present invention, the secondary loadbearing surface of a valve seat is an internal load bearing shoulderthat may be machined as an integral part of the valve seat. In anotherembodiment, the valve seat may include a seal ring insert that comprisesa material having a hardness greater than that of the valve seat. Theseal ring insert may be a solid ring. Alternatively, the seal ring maybe a machined weld bead. In either case, the seal ring insert forms aportion of the valve seat sealing surface and may serve as an internalload bearing shoulder.

[0019] In another embodiment, the secondary load bearing surface of thevalve seat is an external load bearing shoulder. In this embodiment, theflapper closure plate includes a ballast member extending from the endof the flapper closure plate opposite the pivot pin, such that theexternal load bearing shoulder of the valve seat and the ballast memberof the flapper closure plate define the maximum travel of the flapperclosure plate. The external load bearing shoulder may be used alone orin combination with an internal load bearing shoulder or internalsupport members, each serving as secondary load bearing surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a more complete understanding of the present invention,including its features and advantages, reference is now made to thedetailed description of the invention, taken in conjunction with theaccompanying drawings of which:

[0021]FIG. 1 is a schematic illustration of an offshore oil or gasproduction platform operating a subsurface safety valve of the presentinvention;

[0022] FIGS. 2A-2B are half sectional views of a subsurface safety valveof the present invention in the valve open position;

[0023] FIGS. 3A-3B are half sectional views of a subsurface safety valveof the present invention in the valve closed position;

[0024]FIG. 4 is a cross sectional view of a valve of the presentinvention in the valve closed position;

[0025]FIG. 5 is a perspective view of a flapper closure plate of a valveof the present invention;

[0026]FIG. 6 is a cross sectional view of a valve of the presentinvention in the valve closed position under typical load conditions;

[0027]FIG. 7 is a cross sectional view of a valve of the presentinvention in the valve closed position under high load conditions;

[0028]FIG. 8 is a cross sectional view of a valve of the presentinvention in the valve closed position under typical load conditions;

[0029]FIG. 9 is a cross sectional view of a valve of the presentinvention in the valve closed position;

[0030]FIG. 10 is a perspective view of a flapper closure plate of avalve of the present invention;

[0031]FIG. 11 is a cross sectional view of a valve of the presentinvention in the valve closed position;

[0032]FIG. 12 is a perspective view of a flapper closure platepositioned against a support member of a valve of the present invention;

[0033]FIG. 13 is a cross sectional view of a valve of the presentinvention in the valve closed position; and

[0034]FIG. 14 is a perspective view of a flapper closure platepositioned against a pair of support members of a valve of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] While the making and using of various embodiments of the presentinvention is discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts whichcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention, and do not delimit the scope of theinvention.

[0036] Referring to FIG. 1, a subsurface safety valve in use with anoffshore oil and gas production platform is schematically illustratedand generally designated 10. A semi-submersible platform 12 is centeredover a submerged oil and gas formation 14 located below sea floor 16.Wellhead 18 is located on deck 20 of platform 12. Well 22 extendsthrough the sea 24 and penetrates the various earth strata includingformation 14 to form wellbore 26. Disposed within wellbore 26 is casing28. Disposed within casing 28 and extending from wellhead 18 isproduction tubing 30. A pair of seal assemblies 32, 34 provide a sealbetween tubing 30 and casing 28 to prevent the flow of production fluidstherebetween. During production, formation fluids enter wellbore 26through perforations 36 of casing 28 and travel into tubing 30 throughsand control device 38 to wellhead 18. Subsurface safety valve 40 islocated within the production tubing 30 and seals the wellhead 18 fromthe well formation 14 in the event of abnormal conditions. Subsurfacesafety valve 40 includes a valve closure mechanism that, duringproduction from formation 14, is maintained in the valve open positionby hydraulic control pressure received from a surface control system 42through a control conduit 44.

[0037] Referring now to FIGS. 2A, 2B, 3A and 3B, a subsurface safetyvalve 50 is illustrated. Safety valve 50 has a relatively largerproduction bore and is, therefore, intended for use in high flow ratewells. Safety valve 50 is connected directly in series with productiontubing 30. Hydraulic control pressure is conducted in communication witha longitudinal bore 52 formed in the sidewall of the top connector sub54. Pressurized hydraulic fluid is delivered through the longitudinalbore 52 into an annular chamber 56 defined by a counterbore 58 which isin communication with an annular undercut 60 formed in the sidewall ofthe top connector sub 54. An inner housing mandrel 62 is slidablycoupled and sealed to the top connector sub 54 by a slip union 64 andseal 66, with the undercut 60 defining an annulus between inner mandrel62 and the sidewall of top connector sub 54.

[0038] A piston 68 is received in slidable, sealed engagement againstthe internal bore of inner mandrel 62. The undercut annulus 60 opensinto a piston chamber 70 in the annulus between the internal bore of aconnector sub 72 and the external surface of piston 68. The externalradius of an upper sidewall piston section 74 is machined and reduced todefine a radial clearance between piston 68 and connector sub 72. Anannular sloping surface 76 of piston 68 is acted against by thepressurized hydraulic fluid delivered through control conduit 44. InFIGS. 2A-2B, piston 68 is fully extended with the piston shoulder 78engaging the top annular face 80 of an operator tube 82. In this valveopen position, a return spring 84 is fully compressed.

[0039] In the illustrated embodiment, a flapper plate 86 is pivotallymounted onto a hinge sub 88 which is threadably connected to the lowerend of spring housing 90. A valve seat 92 is confined within acounterbore formed on hinge sub 88. The lower end of safety valve 50 isconnected to production tubing 30 by a bottom sub connector 94. Thebottom sub connector 94 has a counterbore 96 which defines a valvechamber 98. Thus, the bottom sub connector 94 forms a part of the valvehousing enclosure. Flapper plate 86 pivots about pivot pin 100 and isbiased to the valve closed position as shown in FIGS. 3A-3B by coilspring 102. In the valve open position as shown in FIGS. 2A-2B, thespring bias force is overcome and flapper plate 86 is retained in thevalve open position by operator tube 82 to permit formation fluid flowup through tubing 30.

[0040] When an out of range condition occurs and subsurface safety valve50 must be operated from the valve open position to the valve closedposition, hydraulic pressure is released from conduit 44 such thatreturn spring 84 acts on the lower end of piston 68 which retractsoperator tube 82 longitudinally through valve chamber 98. Flapperclosure plate 86 will then rotate through chamber 98. As flapper closureplate 86 nears the valve closed position within valve chamber 98 wheresignificant throttling of fluid flow occurs, the high magnitude reactionforces may distort the operator tube 82, flapper closure plate 86 orpivot pin 100. Moreover, the alignment of flapper plate 86 relative tovalve seat 92 may be disturbed in response to slamming impact of flapperclosure plate 86 against valve seat 92.

[0041] Referring now to FIG. 4, a valve is depicted and generallydesignated 120. Valve 120 includes a valve closure mechanism which isdepicted as flapper closure plate 122. Valve 120 also includes a valveseat 124. In the illustrated embodiment, the sealing surfaces of flapperclosure plate 122 and valve seat 124 have mating segments which arematched in curvature to provide a metal-to-metal seal. Sealing surface126 of valve seat 124 is a concave spherical segment. Sealing surface128 of flapper closure plate 122 is a convex spherical segment. Convexflapper closure plate sealing surface 128 and concave valve seat sealingsurface 126 are both generally a surface of revolution produced byrevolving a semi-circular arc having an arc length 130 and radius ofcurvature 132. As shown in FIG. 4, the radius of curvature of convexflapper closure plate sealing surface 128 is substantially equal to theradius of curvature of concave valve seat sealing surface 126.

[0042] Specifically, the spherical radius of curvature of the concavevalve seat sealing surface 126 is matched with the spherical radius ofcurvature of the convex flapper closure plate sealing surface 128. Asused herein, “matched radius of curvature” means that the radius ofcurvature of the flapper plate convex sealing surface 128 issubstantially the same as, but not greater than, the radius of curvatureof the concave valve seat sealing surface 126. Preferably, the convexand concave surfaces are matched in curvature to provide smooth,non-binding surface engagement of convex flapper closure plate sealingsurface 128 against concave valve seat sealing surface 126. The matchingconvex and concave spherical surfaces 128, 126 are lapped together topermit close nesting engagement of flapper closure plate 122 withinvalve seat 124. This arrangement permits smooth angular displacement offlapper closure plate 122 relative to valve seat 124 withoutinterrupting surface-to-surface engagement therebetween.

[0043] Valve seat 124 includes a secondary load bearing surface which,in the illustrated embodiment, is an internal load bearing shoulder 134extending generally radially inwardly from concave valve seat sealingsurface 126. As explained in more detail below, internal load bearingshoulder 134 defines the maximum travel of flapper closure plate 122relative to valve seat 124.

[0044] Referring now to FIG. 5, flapper closure plate 122 has a convexspherical sealing surface 128 and a semi-cylindrical channel 136 acrossthe top of flapper closure plate 122 in alignment with its longitudinalaxis 138. The radial projection of flapper closure plate 122 isminimized, so that in the valve open position as shown in FIGS. 2A-2B,operator tube 82 is received within semi-cylindrical channel 136, withconvex spherical sealing surface 128 projecting into the annulus betweenoperator tube 82 and bottom sub connector 94. Flapper closure plate 122has a secondary load bearing surface depicted as shoulders 142.

[0045] Referring now to FIGS. 6 and 7, valve 120 is depicted in a viewthat is rotated 90 degrees from that in FIG. 4. Valve 120 includesflapper closure plate 122 and valve seat 124. As explained above withreference to FIG. 4, sealing surface 126 of valve seat 124 is a concavespherical segment and sealing surface 128 of flapper closure plate 122is a convex spherical segment. Concave sealing surface 126 of valve seat124 has a radius of curvature that is substantially equal to that ofconvex flapper closure plate sealing surface 128. Valve seat 124includes an internal load bearing shoulder 134 extending generallyradially inwardly from concave valve seat sealing surface 126 whichdefines the maximum travel of flapper closure plate 122 relative tovalve seat 124.

[0046] Under typical flow rate regimes, the matching convex and concavespherical surfaces 128, 126 are lapped together to permit close nestingengagement of flapper closure plate 122 within valve seat 124 as shownin FIG. 6 wherein a gap 140 exists between shoulders 142 of flapperclosure plate 122 and internal load bearing shoulder 134 of valve seat124. In applications where large diameter tubing and large diameterflapper closure plates are necessary and where the ratio of the outerand inner diameters of the sealing surfaces are low, the loads onflapper closure plate 122 tend to deform flapper closure plate 122 aboutaxis 138 which may result in a loss of seal. Specifically, as flapperclosure plate 122 deforms about axis 138, the seal area between flapperclosure plate 122 and valve seat 124 could be reduced. As best seen inFIG. 7, internal load bearing shoulder 134 of valve seat 124 defines themaximum travel of flapper closure plate 122 such that any deformation offlapper closure plate 122 about axis 138 that closes gap 140 betweenshoulders 142 of flapper closure plate and internal load bearingshoulder 134 of valve seat 124 will not reduce the seal area betweenflapper closure plate 122 and valve seat 124 and will not interruptsurface-to-surface engagement between the nested spherical segments, butwill merely shift the region of overlapping engagement. Consequently, acontinuous, positive metal-to-metal seal is maintained completely aroundthe spherical segment interface.

[0047] Referring next to FIG. 8, therein is depicted another embodimentof a valve of the present invention that is generally designated 150.Valve 150 has valve closure member shown as a flapper closure plate 122and valve seat 152. As with valve 120 of FIGS. 6 and 7, valve seat 152has concave valve seat sealing surface 126 and flapper closure plate 122has a convex flapper closure plate sealing surface 128. Concave sealingsurface 126 of valve seat 152 has a radius of curvature that issubstantially equal to that of convex flapper closure plate sealingsurface 128.

[0048] Valve seat 152 includes a seal ring insert 154. Seal ring insert154 forms a portion of concave sealing surface 126 and forms thesecondary load bearing surface illustrated as internal load bearingshoulder 134 that extends generally radially inwardly from concave valveseat sealing surface 126. Internal load bearing shoulder 134 defines themaximum travel of flapper closure plate 122 relative to valve seat 152.Preferably, seal ring insert 154 comprises a material that has a higherhardness than valve seat 152. As seal ring insert 154 must withstandextreme loads exerted by shoulders 142 of flapper closure plate 122, thehardness of seal ring insert 154 is an important feature of the presentinvention. For example, seal ring insert 154 may be formed by machiningout a section of valve seat 152 and laying a weld bead therein. The weldbead is then machined smooth to form a portion of concave sealingsurface 126 and internal load bearing shoulder 134. Alternatively, sealring insert 154 may be a solid ring that is welded in place within valveseat 152 then machined smooth to form a portion of concave sealingsurface 126 and internal load bearing shoulder 134.

[0049] Referring now to FIG. 9, a valve is depicted and generallydesignated 160. Valve 160 includes a valve closure member shown as aflapper closure plate 162 and a valve seat 164. In the illustratedembodiment, the sealing surfaces of flapper closure plate 162 and valveseat 164 have mating segments which are matched in curvature to providea metal-to-metal seal. Sealing surface 166 of valve seat 164 is aconcave spherical segment. Sealing surface 168 of flapper closure plate162 is a convex spherical segment. The radius of curvature 170 of convexflapper closure plate sealing surface 168 is substantially equal to theradius of curvature of concave valve seat sealing surface 166.

[0050] Specifically, the radius of curvature of the flapper plate convexsealing surface 168 is substantially the same as, but not greater than,the radius of curvature of the concave valve seat sealing surface 166.Preferably, the convex and concave surfaces are matched in curvature toprovide smooth, non-binding surface engagement of convex flapper closureplate sealing surface 168 against concave valve seat sealing surface166. The matching convex and concave spherical surfaces 168, 166 arelapped together to permit close nesting engagement of flapper closureplate 162 within valve seat 164. This arrangement permits smooth angulardisplacement of flapper closure plate 162 relative to valve seat 164without interrupting surface-to-surface engagement therebetween.

[0051] Valve seat 164 includes two secondary load bearing surfaces,specifically an internal load bearing shoulder 172 extending generallyradially inwardly from concave valve seat sealing surface 166 and anexternal load bearing shoulder 174 extending generally radiallyoutwardly from concave valve seat sealing surface 166. Flapper closureplate 162 also includes two secondary load bearing surfaces depicted asshoulders 188 and ballast member 176. External load bearing shoulder 174is axially aligned with ballast member 176 of flapper closure plate 162.Ballast member 176 is integral with flapper closure plate 162 and isdisposed opposite of pivot pin support member 178. Together, thesesecondary load bearing surfaces, internal load bearing shoulder 172 andexternal load bearing shoulder 174, define the maximum travel of flapperclosure plate 162 relative to valve seat 164. It should be noted bythose skilled in the art that even though ballast member 176 is depictedas integral with flapper closure plate 162, a ballast member could beattached to flapper closure plate 162 using a variety of methodsincluding, but not limited to, welding or bolting.

[0052] In application where large diameter tubing and large diameterflapper closure plates are necessary and wherein the ratio between theouter and inner diameters of the sealing surfaces is low, the loads onflapper closure plate 162 tend to deform flapper closure plate 162 aboutboth axis 180 and axis 182, as best seen in FIG. 10. As flapper closureplate 162 deforms about axis 180 and gap 184 is closed, internal loadbearing shoulder 172 of valve seat 164 defines the maximum travel ofshoulders 188 of flapper closure plate 162. Likewise, as flapper closureplate 162 deforms about axis 182 and gap 186 is closed, external loadbearing shoulder 174 of valve seat 162 defines the maximum travel ofballast member 176 of flapper closure plate 162. As such, anydeformation of flapper closure plate 162 about axis 180 or axis 182 willnot reduce the seal area between flapper closure plate 162 and valveseat 164 and will not interrupt surface-to-surface engagement betweenthe nested spherical segments, but will merely shift the region ofoverlapping engagement. Consequently, a continuous, positivemetal-to-metal seal is maintained completely around the sphericalsegment interface.

[0053] Even though FIG. 9 depicts two secondary loads bearings surfaces,internal load bearing shoulder 172 and external load bearing shoulder174, it should be understood that by those skilled in the art that asingle secondary load bearing surface may alternatively be utilized suchas internal load bearing shoulder 172, as explained above with referenceto FIGS. 4-8, or external load bearing shoulder 174.

[0054] Referring now to FIG. 11, a valve is depicted and generallydesignated 200. Valve 200 includes a valve closure mechanism depicted asa flapper closure plate 202 and a valve seat 204. In the illustratedembodiment, the sealing surfaces of flapper closure plate 202 and valveseat 204 have mating segments which are matched in curvature to providea metal-to-metal seal. Sealing surface 206 of valve seat 204 is aconcave spherical segment. Sealing surface 208 of flapper closure plate202 is a convex spherical segment. Convex flapper closure plate sealingsurface 208 and concave valve seat sealing surface 206 are bothgenerally a surface of revolution produced by revolving a semi-circulararc having an arc length 210 and radius of curvature 212. As shown inFIG. 11, the radius of curvature of convex flapper closure plate sealingsurface 208 is substantially equal to the radius of curvature of concavevalve seat sealing surface 206.

[0055] Preferably, the convex and concave surfaces are matched incurvature to provide smooth, non-binding surface engagement of convexflapper closure plate sealing surface 208 against concave valve seatsealing surface 206. The matching convex and concave spherical surfaces208, 206 are lapped together to permit close nesting engagement offlapper closure plate 202 within valve seat 204. This arrangementpermits smooth angular displacement of flapper closure plate 202relative to valve seat 204 without interrupting surface-to-surfaceengagement therebetween.

[0056] Valve seat 204 includes a secondary load bearing surface depictedas internal support member 214 extending generally radially inwardlyabout a portion of the circumference of concave valve seat sealingsurface 206 on the side opposite hinge 216. Internal support member 214is positioned within a pocket 218 cut in concave valve sealing surface206 of valve seat 204. Internal support member 214 is securably attachedwithin pocket 218 using suitable means of such a one or more bolts 220.Internal support member 214 is properly aligned within pocket 218 usingpin 222 that extends into hole 224 of internal support member 214 andhole 226 of valve seat 204. Internal support member 214 defines themaximum travel of flapper closure plate 202 relative to valve seat 204.

[0057] Under typical flow rate regimes, the matching convex and concavespherical surfaces 208, 206 are lapped together to permit close nestingengagement of flapper closure plate 202 within valve seat 204 as shownin FIG. 11 wherein a gap 228 exists between a secondary load bearingsurface 230 of flapper closure plate 202 and surface 232 of internalsupport member 214. In applications where large diameter tubing andlarge diameter flapper closure plates are necessary and where the ratioof the outer and inner diameters of the sealing surfaces are low, theloads on flapper closure plate 202 tend to deform flapper closure plate202 about both axis 234 and axis 236, as best seen in FIG. 12, which mayresult in a loss of seal. Specifically, as flapper closure plate 202deforms about axes 234, 236, the seal area between flapper closure plate202 and valve seat 204 could be reduced. Internal support member 214defines the maximum travel of flapper closure plate 202 such that anydeformation of flapper closure plate 202 closes gap 228 but will notreduce the seal area between flapper closure plate 202 and valve seat204 and will not interrupt surface-to-surface engagement between thenested spherical segments, merely shifting the region of overlappingengagement. Consequently, a continuous, positive metal-to-metal seal ismaintained completely around the spherical segment interface.

[0058] While FIG. 11 has been described with reference to a singlesecondary load bearing surface, i.e., support member 214, it should beunderstood by those skilled in the art that support member 214 may beused in conjunction with an internal load bearing shoulder 134 asdescribed above with reference to FIGS. 4-7 or an external load bearingshoulder 174 as described above with reference to FIGS. 9-10 or both.

[0059] Alternatively, it should be noted that internal support member214 may be secured to flapper closure plate 202 such that when flapperclosure plate 214 is in the closed position, internal support member 214is received within pocket 218 which serves as the secondary load bearingsurface of valve seat 204. In another alternative, internal supportmember 214 may be received within or against a secondary load bearingsurface of the valve housing as opposed to the valve seat 214.

[0060] Referring now to FIG. 13, a valve is depicted and generallydesignated 240. Valve 240 includes a valve closure member depicted as aflapper closure plate 242 and a valve seat 244. In the illustratedembodiment, the sealing surfaces of flapper closure plate 242 and valveseat 244 have mating segments which are matched in curvature to providea metal-to-metal seal. Sealing surface 246 of valve seat 244 is aconcave spherical segment. Sealing surface 248 of flapper closure plate242 is a convex spherical segment. Preferably, the convex and concavesurfaces are matched in curvature to provide smooth, non-binding surfaceengagement of convex flapper closure plate sealing surface 248 againstconcave valve seat sealing surface 246. The matching convex and concavespherical surfaces 248, 246 are lapped together to permit close nestingengagement of flapper closure plate 242 within valve seat 244. Thisarrangement permits smooth angular displacement of flapper closure plate242 relative to valve seat 244 without interrupting surface-to-surfaceengagement therebetween.

[0061] Valve seat 244 includes a secondary load bearing surface depictedas a pair of internal support members 250, 252 extending generallyradially inwardly about portions of the circumference of concave valveseat sealing surface 246. Internal support members 250, 252 arepositioned within pockets 254, 256 cut in concave valve sealing surface246 of valve seat 244. Internal support members 250, 252 are securedwithin pockets 254, 256 using by suitable means such as one or morebolts 258. Internal support member 250 is aligned within pocket 254using a pin 260 that extends between hole 262 of valve seat 244 and hole264 at internal support member 250. Internal support member 252 isaligned within pocket 256 using a pin 266 that extends between hole 268of valve seat 244 and hole 270 of internal support member 252.

[0062] Internal support members 250, 252 define the maximum travel offlapper closure plate 242 relative to valve seat 244. Under typical flowrate regimes, the matching convex and concave spherical surfaces 248,246 are lapped together to permit close nesting engagement of flapperclosure plate 242 within valve seat 244, as shown in FIG. 13, whereingaps 272, 274 exists between secondary load bearing surface 280 offlapper closure plate 242 and internal support members 250, 252. Inapplications where large diameter tubing and large diameter flapperclosure plates are necessary and where the ratio of the outer and innerdiameters of the sealing surfaces are low, the loads on flapper closureplate 242 tend to deform flapper closure plate 242 about both axis 276and axis 278, as best seen in FIG. 14, which may result in a loss ofseal. Specifically, as flapper closure plate 242 deforms about axes 276,278, the seal area between flapper closure plate 242 and valve seat 244could be reduced. Internal support members 250, 252 defines the maximumtravel of flapper closure plate 242 such that any deformation of flapperclosure plate 242 closes gaps 272, 274 but will not reduce the seal areabetween flapper closure plate 242 and valve seat 244 and will notinterrupt surface-to-surface engagement between the nested sphericalsegments, merely shifting the region of overlapping engagement.Consequently, a continuous, positive metal-to-metal seal is maintainedcompletely around the spherical segment interface.

[0063] Even though FIG. 13 has depicted the secondary load bearingsurface as consisting of a pair of internal support members 250, 252, itshould be understood by those skilled in the art that these secondaryload bearing surfaces may be used in conjunction with the othersecondary load bearing surfaces described above including internal loadbearing shoulder 134 of FIG. 4 and external load bearing shoulder 174 ofFIG. 9.

[0064] Alternatively, it should be noted that internal support members250, 252 may be secured to flapper closure plate 242 such that whenflapper closure plate 242 is in the closed position, internal supportmembers 250, 252 are received within pockets 254, 256 which serve as thesecondary load bearing surface of valve seat 244. In anotheralternative, internal support members 250, 252 may be received within oragainst a secondary load bearing surface of the valve housing as opposedto the valve seat 244.

[0065] While this invention has been described with a reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments as well as other embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto the description. It is, therefore, intended that the appended claimsencompass any such modifications or embodiments.

What is claimed is:
 1. A valve comprising: a valve housing; a valveclosure mechanism disposed within the valve housing having a valveclosure mechanism sealing surface and a valve closure mechanismsecondary load bearing surface; a valve seat disposed within the valvehousing having a valve seat sealing surface; and a valve secondary loadbearing surface for receiving the valve closure mechanism secondary loadbearing surface.
 2. The valve as recited in claim 1 wherein the valvesecondary load bearing surface is supported by the valve seat.
 3. Thevalve as recited in claim 1 wherein the valve secondary load bearingsurface is supported by the valve housing.
 4. The valve as recited inclaim 1 wherein the valve secondary load bearing surface furthercomprises an internal load bearing shoulder.
 5. The valve as recited inclaim 1 wherein the valve secondary load bearing surface furthercomprises an external load bearing surface.
 6. The valve as recited inclaim 1 wherein the valve secondary load bearing surface furthercomprises an internal support member.
 7. The valve as recited in claim 1wherein the valve secondary load bearing surface further comprises firstand second internal support members.
 8. The valve as recited in claim 1wherein the valve secondary load bearing surface further comprises aninternal support member and an internal load bearing shoulder.
 9. Thevalve as recited in claim 1 wherein the valve secondary load bearingsurface further comprises first and second internal support members andan internal load bearing shoulder.
 10. The valve as recited in claim 1wherein the valve secondary load bearing surface further comprises aninternal support member and an external load bearing surface.
 11. Thevalve as recited in claim 1 wherein the valve secondary load bearingsurface further comprises first and second internal support members andan external load bearing surface.
 12. The valve as recited in claim 1wherein the valve secondary load bearing surface further comprises aseal ring insert within the valve seat.
 13. The valve as recited inclaim 12 wherein the seal ring insert further comprises a solid ring.14. The valve as recited in claim 12 wherein the seal ring insertfurther comprises a machined weld bead.
 15. A valve comprising: a valvehousing having a valve chamber; a valve seat mounted within the housinghaving a valve seat sealing surface, the valve seat defining a flowpassage therethrough; and a flapper closure plate rotatably disposedwithin the valve chamber rotatable between a valve open position inwhich the flapper closure plate is removed from the valve seat and avalve closed position in which a sealing surface of the flapper closureplate sealingly engages the valve seat sealing surface for preventingflow through the flow passage, a valve secondary load bearing surfacereceiving a flapper closure plate secondary load bearing surface todefine the maximum travel of the flapper closure plate in the closedposition.
 16. The valve as recited in claim 15 wherein the valvesecondary load bearing surface is supported by the valve seat.
 17. Thevalve as recited in claim 15 wherein the valve secondary load bearingsurface is supported by the valve housing.
 18. The valve as recited inclaim 15 wherein the secondary load bearing surface further comprises aninternal load bearing shoulder.
 19. The valve as recited in claim 15wherein the valve secondary load bearing surface further comprises anexternal load bearing surface.
 20. The valve as recited in claim 19wherein the flapper closure plate further comprises a ballast member andwherein the external load bearing surface of the valve seat and theballast member of the flapper closure plate define the maximum travel ofthe flapper closure plate in the closed position.
 21. The valve asrecited in claim 15 wherein the valve secondary load bearing surfacefurther comprises an internal support member.
 22. The valve as recitedin claim 15 wherein the valve secondary load bearing surface furthercomprises first and second internal support members.
 23. The valve asrecited in claim 15 wherein the valve secondary load bearing surfacefurther comprises an internal support member and an internal loadbearing shoulder.
 24. The valve as recited in claim 15 wherein the valvesecondary load bearing surface further comprises first and secondinternal support members and an internal load bearing shoulder.
 25. Thevalve as recited in claim 15 wherein the valve secondary load bearingsurface further comprises an internal support member and an externalload bearing surface.
 26. The valve as recited in claim 15 wherein thevalve secondary load bearing surface further comprises first and secondinternal support members and an external load bearing surface.
 27. Thevalve as recited in claim 15 further comprising a seal ring insertwithin the valve seat.
 28. The valve as recited in claim 27 wherein theseal ring insert further comprises a solid ring.
 29. The valve asrecited in claim 27 wherein the seal ring insert further comprises amachined weld bead.
 30. The valve as recited in claim 15 wherein thesealing surface of the flapper closure plate forms a convex sphericalsegment having radius of curvature and wherein the valve seat sealingsurface forms a concave spherical segment having a radius of curvaturethat is substantially matched with the radius of curvature of the convexspherical segment of the flapper closure plate to permit nestingengagement of the convex spherical segment of the flapper closure plateagainst the concave spherical segment of the valve seat.
 31. Asubsurface safety valve adapted to be placed in a well tubing string tocontrol flow therethrough comprising: a valve housing having a boretherethrough; a flapper closure plate mounted within the bore of thehousing and movable between a valve open position and a valve closedposition, the flapper closure plate having a sealing surface and asecondary load bearing surface; an operator movably disposed within thebore of the housing for controlling movement of the flapper closureplate between the valve open position and the valve closed position; avalve seat disposed within the valve housing, the valve seat having aflow passage bore and a sealing surface, in the valve closed position,the sealing surface of the flapper closure plate sealingly engaging thesealing surface of the valve seat; a valve secondary load bearingsurface receiving the secondary load bearing surface of the flapperclosure plate to define the maximum travel of the flapper closure plate.32. The subsurface safety valve as recited in claim 31 wherein the valvesecondary load bearing surface is supported by the valve seat.
 33. Thesubsurface safety valve as recited in claim 31 wherein the valvesecondary load bearing surface is supported by the valve housing. 34.The subsurface safety valve as recited in claim 31 wherein the valvesecondary load bearing surface further comprises an internal loadbearing shoulder.
 35. The subsurface safety valve as recited in claim 31wherein the valve secondary load bearing surface further comprises anexternal load bearing surface.
 36. The subsurface safety valve asrecited in claim 35 wherein the flapper closure plate further comprisesa ballast member and wherein the external load bearing surface of thevalve seat and the ballast member of the flapper closure plate definingthe maximum travel of the flapper closure plate in the closed position.37. The subsurface safety valve as recited in claim 31 wherein the valvesecondary load bearing surface further comprises an internal supportmember.
 38. The subsurface safety valve as recited in claim 31 whereinthe valve secondary load bearing surface further comprises first andsecond internal support members.
 39. The subsurface safety valve asrecited in claim 31 wherein the valve secondary load bearing surfacefurther comprises an internal support member and an internal loadbearing shoulder.
 40. The subsurface safety valve as recited in claim 31wherein the valve secondary load bearing surface further comprises firstand second internal support members and an internal load bearingshoulder.
 41. The subsurface safety valve as recited in claim 31 whereinthe valve secondary load bearing surface further comprises an internalsupport member and an external load bearing surface.
 42. The subsurfacesafety valve as recited in claim 31 wherein the valve secondary loadbearing surface further comprises first and second internal supportmembers and an external load bearing surface.
 43. The subsurface safetyvalve as recited in claim 31 further comprising a seal ring insertwithin the valve seat.
 44. The subsurface safety valve as recited inclaim 42 wherein the seal ring insert further comprises a solid ring.45. The subsurface safety valve as recited in claim 42 wherein the sealring insert further comprises a machined weld bead.
 46. The subsurfacesafety valve as recited in claim 31 wherein the sealing surface of theflapper closure plate forms a convex spherical segment having radius ofcurvature and wherein the valve seat sealing surface forms a concavespherical segment having a radius of curvature that is substantiallymatched with the radius of curvature of the convex spherical segment ofthe flapper closure plate to permit nesting engagement of the convexspherical segment of the flapper closure plate against the concavespherical segment of the valve seat.